Sir James Chadwick

Sir James Chadwick
(1891-1974)

Born in Bollington, England. Intended to study math, but entered
physics line by mistake in 1908, and ended up with a Master of
Science from the University of Manchester, 1912. Thereupon he
received a Research Student Fellowship, which led him to Berlin.
There he worked with Geiger, whose famous Geiger counter
Chadwick employed, within a few months of arriving, for an
important discovery concerning the beta radiation spectrum, at age
23. This discovery was doubted by almost all physicists but
(Rutherford and) Einstein,who found the discovery quite important
and enigmatic, after Chadwick explained it to him in German.
Chadwick was interned months later, after the start of WWI,
throughout which he suffered from malnutrition, leaving him in poor
health for much of the rest of his life. The Germans did allow him to
continue his research, and he examined, among other things,
German radioactive toothpaste.
Liberated after the 1918 armistice, he was swiftly hired by
Rutherford at the Cavendish Laboratory, Cambridge. There
Chadwick succeeded in proving the correctness of Rutherford's
theory, that an element's atomic number is equal to the charge of its
nucleus, ie. that protons exist. He received his Ph.D. in 1921, and
two years later was named the first ever Assistant Director of
Physics Research, becoming the de facto Director as Rutherford
aged.
After a search lasting eight years he discovered the neutron in
1932, and, largely for this achievement, would always be known as
the ideal experimentalist; Madame Curie's daughter might have
preceded Chadwick in this, but she incorrectly interpreted her
results. This discovery, while immediately seen to be important, has
been particularly underrated from the standpoint of its timing, since
subsequent history may have been quite different had the neutron been
discovered even a year later than it was. Had the ensuring breakthroughs
in nuclear physics, such as the creation of the first chain reaction,
been likewise delayed even a year, the A-bomb might have been ready
for use, non in August 1945, but in August 1946, too late to have been
used against Japan. Without the memory of the
horror of Hiroshima to deter war between the Soviets and the West,
such a war probably would have occurred; one way or the other, such
a war would have made the world a very different place than it is now.

In 1935 Chadwick left Cambridge for the University of Liverpool,
where he used his Nobel Prize money to buy a cycletron, and, after
the start of WWII, he explored the possibility of building an A-
bomb; his motivation was a concern that the Allies would be naked if
Heisenberg etc. could build a bomb for Hitler.

After the outbreak of WWII, he was chief advisor to the group of
British officials weighing the option of investing much of Britain's
limited resources in development of an atomic bomb. His reputation
in the U.S. for cautious judgement was such that, when his "MAUD
Report" reached the U.S., the report persuaded administration
officials of the feasibility of a fission device even before Pearl
Harbor. As the British official history later put it, in Spring 1941,U.S.
officials "urged that Chadwick, with his great prestige, should
go to
America. 'Send Chadwick' was the call from Washington--a call that
was to be repeated to great effect in 1943". H.M. Government
preferred to retain Chadwick to keep alive the native bomb program
in the U.K., a decision later regretted; by the time Chadwick arrived
in the U.S, the need for his expertise and stature had become less
desperate.

See

Brown, Andrew, The Neutron and the Bomb (Oxford, 1997) the first
(but major) biography of Chadwick;

reviews of this book include
Calder, Nigel, "The Accidental Physicist", New Scientist,
12 July 1997

Gowing, Margaret, Britain and Atomic Energy 1939-1945,
the official history of the British bomb effort
Groves, Gen. Leslie, Now It Can Be Told (Harper, 1962)
and
Lawren, William, The General and the Bomb: A Biography of
General Leslie R. Groves, Director of the Manhattan Project (Dodd,
Mead & Co., 1988)